Não é possível acessar o servidor web Apache da rede doméstica local

Estou executando um servidor web Apache em uma máquina desktop executando o Trisquel 8 (baseado no Ubuntu). Eu gostaria de tornar o servidor acessível a outras máquinas/dispositivos na minha rede local, mas não consigo descobrir como.

Quando tento me conectar de outro dispositivo, usando o endereço IP local do servidor Apache, recebo mensagens de erro no navegador, como: no Firefox em um Mac, recebo 'Não foi possível conectar. O Firefox não pode estabelecer uma conexão com o servidor em localhost.'. Se eu tentar conectar usando o navegador DuckDuckGo em um telefone Android, recebo 'Página da Web não disponível. A página da Web em http://localhost/ não pôde ser carregada porque: net::ERR_CONNECTION_REFUSED'.

Uma das respostas sugerida usar nmappara ver quais portas estão abertas, que retornou o seguinte resultado:

$ nmap [LOCAL IP ADDRESS]

Starting Nmap 7.01 ( https://nmap.org ) at 2019-10-12 09:25 EDT
Nmap scan report for [LOCAL IP ADDRESS]
Host is up (0.00013s latency).
Not shown: 998 closed ports
PORT   STATE SERVICE
22/tcp open  ssh
80/tcp open  http

Nmap done: 1 IP address (1 host up) scanned in 0.09 seconds

Então, mostra que a porta 80 está aberta para http. Provavelmente também vale a pena mencionar que posso pingar a máquina de outra na rede local e, como mostra a saída do nmap, tenho outra porta aberta para ssh. Eu tenho ssh-ing para esta máquina por vários meses e isso funciona muito bem. Para isso, acabei de instalar o ssh-server e funcionou praticamente fora da caixa.

Então, isso implica que algo está errado com a configuração do Apache2 (em oposição ao iptables/firewall), dado que o ssh está funcionando sem problemas?

Conteúdo do iptables:

$ sudo iptables -L
Chain INPUT (policy ACCEPT)
target     prot opt source               destination         
ACCEPT     tcp  --  anywhere             anywhere             tcp dpt:http ctstate NEW,ESTABLISHED

Chain FORWARD (policy ACCEPT)
target     prot opt source               destination         

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination         

Conteúdo do apache2.conf:

# This is the main Apache server configuration file.  It contains the
# configuration directives that give the server its instructions.
# See http://httpd.apache.org/docs/2.4/ for detailed information about
# the directives and /usr/share/doc/apache2/README.Debian about Debian specific
# hints.
#
#
# Summary of how the Apache 2 configuration works in Debian:
# The Apache 2 web server configuration in Debian is quite different to
# upstream's suggested way to configure the web server. This is because Debian's
# default Apache2 installation attempts to make adding and removing modules,
# virtual hosts, and extra configuration directives as flexible as possible, in
# order to make automating the changes and administering the server as easy as
# possible.

# It is split into several files forming the configuration hierarchy outlined
# below, all located in the /etc/apache2/ directory:
#
#       /etc/apache2/
#       |-- apache2.conf
#       |       `--  ports.conf
#       |-- mods-enabled
#       |       |-- *.load
#       |       `-- *.conf
#       |-- conf-enabled
#       |       `-- *.conf
#       `-- sites-enabled
#               `-- *.conf
#
#
# * apache2.conf is the main configuration file (this file). It puts the pieces
#   together by including all remaining configuration files when starting up the
#   web server.
#
# * ports.conf is always included from the main configuration file. It is
#   supposed to determine listening ports for incoming connections which can be
#   customized anytime.
#
# * Configuration files in the mods-enabled/, conf-enabled/ and sites-enabled/
#   directories contain particular configuration snippets which manage modules,
#   global configuration fragments, or virtual host configurations,
#   respectively.
#
#   They are activated by symlinking available configuration files from their
#   respective *-available/ counterparts. These should be managed by using our
#   helpers a2enmod/a2dismod, a2ensite/a2dissite and a2enconf/a2disconf. See
#   their respective man pages for detailed information.
#
# * The binary is called apache2. Due to the use of environment variables, in
#   the default configuration, apache2 needs to be started/stopped with
#   /etc/init.d/apache2 or apache2ctl. Calling /usr/bin/apache2 directly will not
#   work with the default configuration.


# Global configuration
#

#
# ServerRoot: The top of the directory tree under which the server's
# configuration, error, and log files are kept.
#
# NOTE!  If you intend to place this on an NFS (or otherwise network)
# mounted filesystem then please read the Mutex documentation (available
# at <URL:http://httpd.apache.org/docs/2.4/mod/core.html#mutex>);
# you will save yourself a lot of trouble.
#
# Do NOT add a slash at the end of the directory path.
#
#ServerRoot "/etc/apache2"

#
# The accept serialization lock file MUST BE STORED ON A LOCAL DISK.
#
Mutex file:${APACHE_LOCK_DIR} default

#
# PidFile: The file in which the server should record its process
# identification number when it starts.
# This needs to be set in /etc/apache2/envvars
#
PidFile ${APACHE_PID_FILE}

#
# Timeout: The number of seconds before receives and sends time out.
#
Timeout 300

#
# KeepAlive: Whether or not to allow persistent connections (more than
# one request per connection). Set to "Off" to deactivate.
#
KeepAlive On

#
# MaxKeepAliveRequests: The maximum number of requests to allow
# during a persistent connection. Set to 0 to allow an unlimited amount.
# We recommend you leave this number high, for maximum performance.
#
MaxKeepAliveRequests 100

#
# KeepAliveTimeout: Number of seconds to wait for the next request from the
# same client on the same connection.
#
KeepAliveTimeout 5


# These need to be set in /etc/apache2/envvars
User ${APACHE_RUN_USER}
Group ${APACHE_RUN_GROUP}

#
# HostnameLookups: Log the names of clients or just their IP addresses
# e.g., www.apache.org (on) or 204.62.129.132 (off).
# The default is off because it'd be overall better for the net if people
# had to knowingly turn this feature on, since enabling it means that
# each client request will result in AT LEAST one lookup request to the
# nameserver.
#
HostnameLookups Off

# ErrorLog: The location of the error log file.
# If you do not specify an ErrorLog directive within a <VirtualHost>
# container, error messages relating to that virtual host will be
# logged here.  If you *do* define an error logfile for a <VirtualHost>
# container, that host's errors will be logged there and not here.
#
ErrorLog ${APACHE_LOG_DIR}/error.log

#
# LogLevel: Control the severity of messages logged to the error_log.
# Available values: trace8, ..., trace1, debug, info, notice, warn,
# error, crit, alert, emerg.
# It is also possible to configure the log level for particular modules, e.g.
# "LogLevel info ssl:warn"
#
LogLevel warn

# Include module configuration:
IncludeOptional mods-enabled/*.load
IncludeOptional mods-enabled/*.conf

# Include list of ports to listen on
Include ports.conf


# Sets the default security model of the Apache2 HTTPD server. It does
# not allow access to the root filesystem outside of /usr/share and /var/www.
# The former is used by web applications packaged in Debian,
# the latter may be used for local directories served by the web server. If
# your system is serving content from a sub-directory in /srv you must allow
# access here, or in any related virtual host.
<Directory />
        Options FollowSymLinks
        AllowOverride None
        Require all denied
</Directory>

<Directory /usr/share>
        AllowOverride None
        Require all granted
</Directory>

<Directory /var/www/>
        Options Indexes FollowSymLinks
        AllowOverride All
#       Require local
#       Require ip 192.168.1
        Require all granted
</Directory>

#<Directory /srv/>
#       Options Indexes FollowSymLinks
#       AllowOverride None
#       Require all granted
#</Directory>




# AccessFileName: The name of the file to look for in each directory
# for additional configuration directives.  See also the AllowOverride
# directive.
#
AccessFileName .htaccess

#
# The following lines prevent .htaccess and .htpasswd files from being
# viewed by Web clients.
#
<FilesMatch "^\.ht">
        Require all denied
</FilesMatch>


#
# The following directives define some format nicknames for use with
# a CustomLog directive.
#
# These deviate from the Common Log Format definitions in that they use %O
# (the actual bytes sent including headers) instead of %b (the size of the
# requested file), because the latter makes it impossible to detect partial
# requests.
#
# Note that the use of %{X-Forwarded-For}i instead of %h is not recommended.
# Use mod_remoteip instead.
#
LogFormat "%v:%p %h %l %u %t \"%r\" %>s %O \"%{Referer}i\" \"%{User-Agent}i\"" vhost_combined
LogFormat "%h %l %u %t \"%r\" %>s %O \"%{Referer}i\" \"%{User-Agent}i\"" combined
LogFormat "%h %l %u %t \"%r\" %>s %O" common
LogFormat "%{Referer}i -> %U" referer
LogFormat "%{User-agent}i" agent

# Include of directories ignores editors' and dpkg's backup files,
# see README.Debian for details.

# Include generic snippets of statements
IncludeOptional conf-enabled/*.conf

# Include the virtual host configurations:
IncludeOptional sites-enabled/*.conf

# vim: syntax=apache ts=4 sw=4 sts=4 sr noet

Eu preciso do AllowOverride Allunder /var/wwwporque estou tentando executar uma instância do Wordpress e precisa ser capaz de gravar no servidor Apache.

O Apache2 está definitivamente em execução, pois posso acessar o conteúdo da web usando 'localhost' de um navegador na máquina local. Além disso, systemctl status apache2mostra que está em execução:

~$ systemctl status apache2
● apache2.service - LSB: Apache2 web server
   Loaded: loaded (/etc/init.d/apache2; bad; vendor preset: enabled)
  Drop-In: /lib/systemd/system/apache2.service.d
           └─apache2-systemd.conf
   Active: active (running) since Thu 2019-10-10 20:01:44 EDT; 5min ago
     Docs: man:systemd-sysv-generator(8)
  Process: 1562 ExecStart=/etc/init.d/apache2 start (code=exited, status=0/SUCCESS)
   CGroup: /system.slice/apache2.service
           ├─1621 /usr/sbin/apache2 -k start
           ├─1624 /usr/sbin/apache2 -k start
           ├─1625 /usr/sbin/apache2 -k start
           ├─1626 /usr/sbin/apache2 -k start
           ├─1627 /usr/sbin/apache2 -k start
           ├─1628 /usr/sbin/apache2 -k start
           └─2102 /usr/sbin/apache2 -k start

Oct 10 20:01:42 lee-Desktop systemd[1]: Starting LSB: Apache2 web server...
Oct 10 20:01:42 lee-Desktop apache2[1562]:  * Starting Apache httpd web server apache2
Oct 10 20:01:43 lee-Desktop apache2[1562]: AH00558: apache2: Could not reliably determine the server's fully qualified domain name, using 127.0.1.1. Set the 'ServerName' directive globally to suppress this message
Oct 10 20:01:44 lee-Desktop apache2[1562]:  *
Oct 10 20:01:44 lee-Desktop systemd[1]: Started LSB: Apache2 web server.

Conforme sugerido nos comentários, tentei netstat --inet -a | grep apache2, mas não retornou nada. Aparentemente, isso é incomum se o apache2 estiver em execução, pois deve estar ouvindo na porta 80. Corri netstat -plunt | grep :80e obtive a seguinte saída:

$ sudo netstat -plunt | grep :80
tcp6       0      0 :::80                   :::*                    LISTEN      1557/apache2    

Isso significa que o Apache está ouvindo, mas não está ouvindo nada?

Em termos das configurações do virtualhost, que também foram solicitadas, o único arquivo /etc/apache2/sites-enabled/é 000-default.conf, cujo conteúdo é:

<VirtualHost *:80>
        # The ServerName directive sets the request scheme, hostname and port that
        # the server uses to identify itself. This is used when creating
        # redirection URLs. In the context of virtual hosts, the ServerName
        # specifies what hostname must appear in the request's Host: header to
        # match this virtual host. For the default virtual host (this file) this
        # value is not decisive as it is used as a last resort host regardless.
        # However, you must set it for any further virtual host explicitly.
        #ServerName www.example.com

        ServerAdmin webmaster@localhost
        DocumentRoot /var/www/html

        # Available loglevels: trace8, ..., trace1, debug, info, notice, warn,
        # error, crit, alert, emerg.
        # It is also possible to configure the loglevel for particular
        # modules, e.g.
        #LogLevel info ssl:warn

        ErrorLog ${APACHE_LOG_DIR}/error.log
        CustomLog ${APACHE_LOG_DIR}/access.log combined

        # For most configuration files from conf-available/, which are
        # enabled or disabled at a global level, it is possible to
        # include a line for only one particular virtual host. For example the
        # following line enables the CGI configuration for this host only
        # after it has been globally disabled with "a2disconf".
        #Include conf-available/serve-cgi-bin.conf
</VirtualHost>

# vim: syntax=apache ts=4 sw=4 sts=4 sr noet

Eu também tentei executar tail -f /var/log/apache2/*.log, mas nada está sendo impresso nos logs quando tento conectar de uma máquina remota.

Então, como posso solucionar o que está bloqueando a conexão? Existe um log em algum lugar que possa me esclarecer por que a conexão está sendo recusada e por qual motivo?

Tentei as sugestões feitas por Jacob em sua resposta, mas infelizmente não resolveu o problema. Qualquer outra sugestão ou orientação seria muito apreciada!